I have on 08 E92 6MT without tech package (no MDM)...not sure if that makes any difference.

During a recent tech inspection I was shown that the rear wheels spin independently. Certainly not normal for most LSD's, but I asked if that could be due to the electronics in the diff. A few phone calls later I got the answer that the diff will not engage unless that car is running and there is load. Further, that the only way to really test it was to do some burnouts. So we did and I was never able to lay down 2 visible tire marks (straight line from standing start or around corners).

My question is how can one test the diff to see if it is functioning properly?